Geometric measurement system and method of measuring a geometric characteristic of an object

ABSTRACT

A geometric measurement system is adapted to precisely measure one or more surfaces of objects such as corneas, molds, contact lenses in molds, contact lenses, or other objects in a fixture. The geometric measurement system can employ one or more of three possible methods of measurement: Shack-Hartmann wavefront sensing with wavefront stitching; phase diversity sensing; and white light interferometry.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims the priority benefit under 35 U.S.C. §119(e) from U.S. provisional patent application 60/789,901 filed on 7Apr. 2006 in the names of Daniel Neal et al., the entirety of which ishereby incorporated herein by reference for all purposes as if fully setforth herein.

BACKGROUND AND SUMMARY

1. Field

This invention pertains to the field of measurements, and moreparticularly, to a geometric measurement system and a method of makinggeometric measurements of an object using light reflected and/orrefracted from one or more surfaces of the object.

2. Description

There are many examples of measurement or metrology systems that aredesigned to measure or characterize an object's surface. Among thesesystems are optically-based systems which operate by reflecting orscattering light from the object's surface and then collecting andanalyzing the reflected or scattered light. These systems may use any ofa number of principles such as, but not limited to, interferometry,Moir{acute over (e )}deflectometry, heterodyne interferometry, lasertriangulation, phase diversity wavefront sensing, or Shack-Hartmann(Hartmann-Shack) wavefront sensing. Accurate measurements are possiblewith some of these techniques down to a fraction of a nanometer.

However, many of these techniques are difficult to apply to highlycurved surfaces and/or optically transmissive surfaces. When objectssuch as, but not limited to, a contact lens, contact lens mold, highnumerical aperture optical element, pin, optical lens, inter-ocular lens(IOL), IOL mold, curved mirror, cornea, or another object with a rapidvariation in surface contour is measured, it is very difficult toproject the light onto the entire surface and to collect it back in acontrolled and uniform fashion. Projecting and collecting lens(es) witha very high numerical aperture (NA) are required. Furthermore, whilegood results may be achieved with some of these methods by projectingand then collecting the light from a spherical surface, the degree towhich the surface can depart from spherical is limited by the dynamicrange of the measurement instrument. This severely limits the range ofobjects whose surfaces can be measured since many objects are notspherical but may be highly aspherical.

Also, many objects are optically transmissive at the wavelength of thelight used in the above-mentioned measuring systems. In that case, inprojecting and collecting light from the object, light is collected fromall surfaces simultaneously. The light reflected from various surfacesmixes together and makes interpretation of resulting patterns difficult.The different surfaces may reflect vastly different amounts of lightdepending upon the index of refraction and other conditions of thesurfaces. While it is possible in some cases to spoil the reflection (orotherwise identify it) from the back surface (or other feature that isnot of interest) by painting it black, immersing it in a fluid, orotherwise altering it, this has the effect of damaging the part that isbeing measured. This is not generally desirable in a measurement system.

It is also possible to use a contact profilometer to measure thesurface. Very sophisticated versions of these instruments exist and theyare capable of making very precise measurements. However, it isgenerally not possible to measure two surfaces simultaneously with aprofilometer, and the fact that there is a contact with the surface maydamage the object. In addition, these instruments are very slow and mayhave different precision on rough surfaces than they do for smoothsurfaces.

Neal et al. U.S. Pat. No. 6,184,974 (“Neal et al.”), which isincorporated herein by reference in its entirety as if fully set forthherein, discloses a means for making measurements of a small area of atleast one surface of a silicon wafer or other flat surface and forstitching these measurements together to form a measurement of theentire surface. Neal et al. uses overlap regions to connect themeasurements together and eliminate any effects of instrument inaccuracyduring the measurement process. This same technique has been applied tothe measurement of large telescope mirrors with excellent success(Kiikka et al, “The JWST Infrared Scanning Shack Hartmann System: a newin-process way to measure large mirrors during optical fabrication atTinsley,” SPIE 2006).

It would be desirable to provide a method and system for measuring oneor more geometric characteristics of an object having one or more highlycurved, potentially aspheric and non-symmetric surfaces. It would alsobe desirable to provide a method and system for measuring one or moregeometric characteristics of an object that has at least onesubstantially transparent surface, which can accurately distinguishbetween first and second surface reflections and provide accuratesurface shape maps for each surface.

In one aspect of the invention, a method determines at least onegeometric characteristic of an object having a first surface and asecond surface. The method comprises: (a) adjusting a positionalrelationship between a first surface of the object and a light source toilluminate a subregion of the first surface of the object, whereby aportion of light illuminating the subregion of the first surface of theobject passes through the object to the second surface of the object;(b) delivering light from the subregion of the first surface of theobject to a wavefront sensor while blocking a majority of light from thesecond surface of the object from reaching the wavefront sensor; (c)determining a wavefront of light received from the subregion of thefirst surface with a wavefront sensor; (d) repeating steps (a) through(c) for a plurality of different subregions spanning a measurementregion for the first surface of the object, where adjacent subregionshave an overlapping portion; (e) stitching together the wavefrontsdetermined in each execution of step (c) including derivatives of thewavefronts in the overlapping portions, to construct a wavefront oflight received from the measurement region of the first surface of theobject; and (f) determining at least one shape parameter of the firstsurface of the object from the constructed wavefront.

In another aspect of the invention, a system determines at least onegeometric characteristic of an object. The system comprises: a lightsource; a wavefront sensor; an optical system adapted to deliver lightfrom the light source to a surface to be measured of the object, and todeliver light from the surface to be measured of the object to thewavefront sensor, whereby a portion of the light delivered to thesurface to be measured passes through the object to a surface of theobject that is not being measured; a positioner adapted to adjustrelative positions of the light source and the surface to be measuredsuch that, at each relative position, the light from the light source isdelivered onto a sub-region of the surface to be measured, and lightfrom the sub-region of the surface to be measured is delivered to thewavefront sensor, the positioner adjusting the relative positions suchthat adjacent sub-regions have an overlap portion; and a processoradapted to stitch together wavefronts measured by the wavefront sensorfor different sub-regions of the surface to be measured at the relativepositions provided by the positioner, including using derivatives ofwavefronts in overlap regions, to construct a wavefront of lightreceived from a measurement region of the surface to be measured,wherein the optical system comprises an aperture for blocking a majorityof light from the surface of the object not being measured from reachingthe wavefront sensor.

In yet another aspect of the invention, a method determines at least onegeometric characteristic of an object having a first surface and asecond surface. The method comprises: (a) adjusting a positionalrelationship between a first surface of the object and a light source toilluminate a subregion of the first surface of the object, including atleast one of: rotating the object with respect to the light source,rotating the light source with respect to the object, tilting the objectwith respect to the light source, and tilting the light source withrespect to the object; (b) delivering light from the subregion of thefirst surface of the object to a wavefront sensor; (c) determining awavefront of light received from the subregion of the first surface witha wavefront sensor; (d) repeating steps (a) through (c) for a pluralityof different subregions spanning a measurement region for the firstsurface of the object, where adjacent subregions have an overlappingportion; (e) stitching together the wavefronts determined in eachexecution of step (c) including derivatives of the wavefronts in theoverlapping portions, to construct a wavefront of light received fromthe measurement region of the first surface of the object; and (f)determining at least one shape parameter of the first surface of theobject from the constructed wavefront.

In still another aspect of the invention, a system determines at leastone geometric characteristic of an object, the system comprising: alight source; a wavefront sensor; an optical system adapted to deliverlight from the light source to a surface to be measured of the object,and for delivering light from the surface to be measured of the objectto the wavefront sensor; a positioner adapted to adjust relativepositions of the light source and the surface to be measured such that,at each relative position, the light from the light source is deliveredonto a sub-region of the surface to be measured, and light from thesub-region of the surface to be measured is delivered to the wavefrontsensor, the positioner adjusting the relative positions such thatadjacent sub-regions have an overlap portion, wherein the positionerincludes one of: means for rotating the light source, means for rotatingthe object, means for tilting the light source, and means for tiltingthe object; and a processor adapted to stitch together wavefrontsmeasured by the wavefront sensor for different sub-regions of thesurface to be measured at the relative positions provided by thepositioner, including using derivatives of wavefronts in overlapregions, to construct a wavefront of light received from a measurementregion of the surface to be measured.

In a further aspect of the invention, a system determines at least onegeometric characteristic of an object having a first surface and asecond surface. The system comprises: a light source adapted toilluminate the object; an optical element adapted to receive light fromthe first and second surfaces of the object and to produce a first lightbeam corresponding to light from the first surface and a second lightbeam corresponding to light from the second surface; a light intensitydetector having a radiation sensitive surface adapted to receive thefirst and second light beams and to detect the intensity of incidentradiation on the radiation sensitive surface from the first and secondlight beams, and to produce an output that provides a measure of theintensity of the incident radiation; a positioner adapted to adjustrelative positions of the optical element and the light intensitydetector; and a processor adapted to determine wavefronts of the lightfrom the first and second surfaces based on the output of the lightintensity detector at a plurality of different relative positions.

In a still further aspect of the invention, a method determines at leastone geometric characteristic of an object having a first surface and asecond surface. The method comprises: (a) illuminating the object; (b)transmitting light from the first and second surfaces of the objectthrough an optical element to produce a first light beam correspondingto light from the first surface and a second light beam corresponding tolight from the second surface; (c) detecting the intensity of incidentradiation on a radiation sensitive surface from the first and secondlight beams; (d) adjusting relative positions of the optical element andthe radiation sensitive surface, and at each of a plurality of differentrelative positions producing an output that provides a measure of theintensity of the incident radiation; and (e) determining wavefronts ofthe light from the first and second surfaces of the object based on theoutputs produced at each of the different relative positions.

In yet a further aspect of the invention, a system determines at leastone geometric characteristic of an object having a first surface and asecond surface. The system comprises: a light source adapted toilluminate the object; a diffractive optical element adapted to receivelight from the first and second surfaces of the object and to producetherefrom at least two spatially-separated light distributions having atleast one statistical characteristic different from each other; a lightintensity detector having a radiation sensitive surface adapted toreceive the at least two spatially-separated light distributions, todetect the at least two spatially-separated light distributions atdifferent points across the radiation sensitive surface and to producean output that provides a measure of the intensity of the incidentradiation at the different points; and a processor adapted to determinewavefronts of the light from the first and second surfaces based on theoutput of the light intensity detector.

In still yet another aspect of the invention, a method determines atleast one geometric characteristic of an object having a first surfaceand a second surface. The method comprises: (a) illuminating the object;(b) transmitting light from the first and second surfaces of the objectthrough a diffractive optical element to produce therefrom at least twospatially-separated light distributions having at least one statisticalcharacteristic different from each other; (c) detecting the intensity ofincident radiation on a radiation sensitive surface from the at leasttwo spatially-separated light distributions at different points on theradiation sensitive surface to produce an output that provides a measureof the intensity of the incident radiation at the different points; (d)determining wavefronts of the light from the first and second surfacesof the object based on the output of the detection.

In still yet a further aspect of the invention, a system determines atleast one geometric characteristic of an object. The system comprises: astructure having a reference surface with a known curvature; a stageadapted to hold an object; and an interferometer. The interferometercomprises: a light source adapted to generate light having a broadspectral bandwidth, a detector; a mirror; a beamsplitter adapted toreceive the light from the light source and to divide the light into afirst portion and a second portion; wherein the system is configured toprovide the first portion of the light from the beamsplitter toilluminate the object and the reference surface, and to provide at leastsome of the first portion of the light from the object and the referencesurface to the detector, and wherein the system is configured to providethe second portion of the light from the beamsplitter to illuminate themirror, and to provide at least some of the second portion of the lightfrom the mirror to the detector; and means for adjusting an optical pathlength traveled by the second portion of the light from the beamsplitterto the detector, wherein the detector is adapted to output a signalindicating when an optical path length traveled by the first portion ofthe light from the beam splitter to the detector is the same as theoptical path length traveled by the second portion of the light from thebeamsplitter to the detector.

In another, further aspect of the invention, a method determines atleast one geometric characteristic of an object. The method comprises:(a) generating light having a broad spectral bandwidth; (b) dividing thelight into a first portion and a second portion with a beamsplitter; (c)providing the first portion of the light to a selected region of theobject and to a reference surface of a structure having a knowncurvature; (d) providing at least some of the first portion of the lightfrom the object and the reference surface to a detector; (e) providingthe second portion of the light to a mirror; (f) reflecting the firstportion of the light from the mirror to the detector; (g) passing asecond portion of the light through a reference lens to a selectedregion of a surface to be measured of the object; (h) adjusting anoptical path length traveled by the second portion of the light from thebeamsplitter to the detector until the detector outputs a signalindicating a first interference fringe caused by light refracted orreflected by a first surface of the object; (i) adjusting the opticalpath length traveled by the second portion of the light from thebeamsplitter to the detector until the detector outputs a second signalindicating a second interference fringe caused by light refracted orreflected by a second surface of the object; (j) adjusting the opticalpath length traveled by the second portion of the light from thebeamsplitter to the detector until the detector outputs a second signalindicating a third interference fringe caused by light refracted orreflected by the reference surface; and (k) determining a thickness ofthe object at the selected region from the first, second, and thirdinterference fringes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B functionally illustrate in block-diagram form one embodimentof a system for determining at least one geometric characteristic of anobject;

FIG. 2 functionally illustrates a process of measuring wavefronts from anumber of subregions of an object and stitching the wavefronts togetherto obtain a wavefront from a larger region of the object spanning atleast portions of the subregions;

FIGS. 3A-B illustrate two possible arrangements for a geometricmeasurement system which may be one physical implementation of geometricmeasurement system of FIGS. 1A-B;

FIGS. 4A-C illustrate a geometric measurement instrument, including agoniometer, that may be one structural embodiment of the arrangement ofFIG. 3A;

FIGS. 5A-C are front views illustrating operation of the goniometer ofFIGS. 4A-C;

FIG. 6 illustrates another embodiment of a system for determining atleast one geometric characteristic of an object;

FIG. 7 illustrates yet another embodiment of a system for determining atleast one geometric characteristic of an object; and

FIG. 8 illustrates still another embodiment of a system for determiningat least one geometric characteristic of an object.

DETAILED DESCRIPTION

As discussed above, it is desirable to characterize one or both surfacesof an optically transparent object, or an object having at least onesubstantially transparent surface, however, in general it is difficultto separate the reflection from the front surface from that of the backsurface. However, in the case of a highly curved surface, such as istypical of a contact lens, contact lens mold, aspheric optic, IOL,cornea or other highly curved object, we disclose below systems andmethods for separating the two surfaces in order isolate the surfacesfor measurement and/or to measure the two surfaces (either sequentiallyor simultaneously).

FIGS. 1A-B functionally illustrate one embodiment of a geometricmeasurement system 100 for determining at least one geometriccharacteristic of an object 105, and an associated method of determiningat least one geometric characteristic of the object 105, using awavefront sensor. In particular, the system and method illustrated inFIGS. 1A-B are well suited for determining one or more geometriccharacteristics of a substantially optically transparent object 105having a highly curved surface, such as a contact lens. Geometriccharacteristic(s) of the object 105 that may be characterized by thesystem 100 include shapes of one or both main surfaces 105 a, 105 band/or a thickness profile of the object 105.

Geometric measurement system 100 includes: a light source 110; anoptical system comprising lenses 120 and 130, and a modulator or spatialfilter 125 disposed in an optical path between lenses 120 and 130; abeamsplitter 135; a wavefront sensor 137 including lenslet array 140 anddetector 150; a positioner 163; a secondary positioner 160; and aprocessor 170.

Beneficially, light source 110 is adapted to produce collimated light.Also beneficially, light source 110 is a pulsed light source, which maybe operated under control of processor 170. The light source 110 maymounted separately from the positioners 160, 163 or, alternatively, maybe configured to have a fixed position relative to one of thepositioners 160, 163. It will be appreciated that the light source 110,as well as other light sources discussed herein, may be replaced by asource of electromagnetic radiation outside the visible wavelength band,for example, in the near-infrared, infrared, or ultraviolet bands. Whilethe light source 110 will generally be with a relatively narrowwavelength band, for example, a laser or LED, the light source 110 mayalso include broadband sources.

Beneficially, spatial filter 125 operates to block a majority (i.e.,≧50%) of the reflected and/or refracted light from a surface of object105 not being characterized or measured from reaching wavefront sensor137. Depending upon various factors, including for example thecharacteristics of the surfaces of the object being measured, spatialfilter 125 may operate to block a substantial majority (i.e., ≧90%) ofthe reflected and/or refracted light from the surface of object 105 notbeing characterized or measured from reaching wavefront sensor 137. Inone embodiment, as illustrated in FIGS. 1A-B spatial filter 125 may bean aperture, particularly a range limiting aperture (RLA), having a sizeadapted to operate in conjunction with lens 130 and positioner 163 topass substantially all of the light reflected or refracted from asurface of object 105 that is being measured or characterized, and toblock a majority or a substantial majority of the reflected or refractedlight from a surface of object 105 not being characterized or measuredfrom reaching wavefront sensor 137. Alternatively, spatial filter 125may be a spatial light modulator (such as a transmissive liquid crystaldevice), or other device that can spatially filter or modulate a lightbeam.

Beneficially, lenses 120 and 130 are mounted in an arrangement toprovide an adjustable telescope, for example by means of secondarypositioner 160.

As shown in FIGS. 1A-B, beneficially wavefront sensor 137 is aShack-Hartman wavefront sensor. However, a moire deflectometer, aTscherning aberrometer, or other suitable sensor or interferometer couldbe employed.

Positioner 163 is adapted to adjust the relative positions between: (A)light source 110 and/or wavefront sensor 137 and/or spatial filter 125;and (B) object 105, in particular a surface of the object 105 that isbeing characterized or measured. As used herein, the term “positioner”means a device that is used to control at least one linear and/orrotational position of objects or elements attached to the positioner.In some embodiments, the positioner provides up to six axes of control(e.g., 3 linear axes and three rotational axes). Beneficially,positioner 163 adjusts these relative positions such that, at eachrelative position, light from light source 110 is delivered onto asubregion of the surface to be measured, and light scattered and/orreflected from the subregion of the surface to be measured is deliveredto wavefront sensor 137. Positioner 163 adjusts the relative positionssuch that adjacent subregions scanned on the surface of object 105 havean overlap portion. Positioner 163 may include its own controller, ormay be controlled by processor 170.

Beneficially, positioner 163 is adapted to rotate and/or tilt theoptical system in a goniometrical manner about the center of curvatureof the surface of object 105 being measured, and performs measurementsover a plurality of subregions spanning a desired measurement region(which may be the entire surface of object 105) as will be explained infurther detail below. Positioner 163 also serves to adjust the relativedistance between the measurement system and the first or second surfaces(e.g., the spacing or distance between spatial filter 125 and object105).

Turning to FIG. 1A, to begin a measurement of object 105, positioner 163is controlled to adjust a positional and/or rotational relationshipbetween first surface 105 a of object 105 and light source 110 and/orspatial filter 125 and/or wavefront sensor 137 to illuminate a desiredsubregion of first surface 105 a.

Collimated light from light source 110 is injected via beamsplitter 135and through the relay telescope of lenses 130 and 120. The light isinjected through the spatial filter 125 which in the illustration ofFIGS. 1A-B is shown as an RLA arranged to be one focal length from lens130. Light from lens 130 illuminates a sub-region of first surface 105 aof object 105. Beneficially, the position of lens 120 and/or lens 130 isadjusted so that light reflected from first (e.g. front) surface 105 aof object 105 just matches the convergence (or divergence) of theincident light. Thus, the reflected rays from the subregion of frontsurface 105 a of object 105 retrace (approximately) their injected pathand pass back through spatial filter 125.

The portion of the light that is transmitted through opticallytransparent object 105 is focused by the curvature of surface 105 a, andafter reflection from the second surface 105 b of element 105, isfurther defocused. This light is collected also by lens 120 but ismostly blocked by spatial filter 125 from reaching wavefront sensor 137,since it is not focused in the plane of spatial filter 125. A smallportion of this light will pass through spatial filter 125 and be imagedthrough lens 130, passing through beamsplitter 135, lenslet array 140onto detector 150. Since spatial filter 125 blocks a majority or asubstantial majority of the light from second surface 105 b of object105, the light or signal from first surface 105 a on detector 150 willgenerally be much brighter and will be straightforward to identify.

Detector 150 operates in conjunction with processor 170 to determine awavefront of light received by the wavefront sensor 137 from thesubregion of first surface 105 a of object 105.

Positioner 163 then readjusts the relative position and/or anglebetween: (A) light source 110 and/or spatial filter 125 and/or wavefrontsensor 137; and (B) the surface of object 105 to be measured toilluminate another subregion of the object's first surface 105 a, andwavefront sensor 137 then measures the wavefront from this newsubregion. At this time, beneficially the relay telescope comprisinglenses 120 and 130 may be adjusted to maintain the focus of the light onthe desired subregion of surface 105 a by adjusting secondary positioner160, for example by adjusting the convergence or divergence of lightdirected toward the object 105. This allows for the dynamic range ofwavefront sensor 137 to be greatly extended with respect to defocuserror, which for highly curved surfaces is usually the dominant errorterm. There is a unique relationship between the position of secondarypositioner 160 that controls the separation of lenses 120 and 130 andthe amount of defocus error (also known as spherical optical power) thatis introduced. The amount of defocus, which can be determined by readingout the position of secondary positioner 160 with encoders or some othermethod, is added to the measured wavefront error from wavefront sensor137 comprised of lenslet array 140 and detector 150. Thus even when thesurface of object 105 being measured is highly aspheric and may changeits optical power or curvature rapidly over a small distance, it ispossible to readjust the position of secondary positioner 160 aspositioner 163 scans over different subregions, and always stay withinthe dynamic range of the combined optical system and wavefront sensor137.

FIG. 2 illustrates a process of measuring wavefronts from a plurality ofsubregions of object 105, which wavefronts are then stitched together byprocessor 170 to construct a wavefront of light received from a largerregion of object 105 spanning at least portions of the subregions.Beneficially, as illustrated in FIG. 2, the subregions each include anoverlap portion that is “shared” with another adjacent subregion.Positioner 163 can be controlled to produce a pattern of known sampleregions. This pattern can be regular or irregular, so long as the exactmeasurement region of each is known. Further details of the process ofstitching together the individual wavefronts of subregions to constructa wavefront of a larger region are disclosed in Neal et al. U.S. Pat.No. 6,184,974, which has already been incorporated herein by reference.

Turning now to FIG. 1B, to measure or characterize second surface 105 bof object 105, the relative distance between the object 105 and lens 120and/or spatial filter 125 is adjusted until the light reflected fromsecond surface 105 b passes through the spatial filter 125 by retracingits path through the optical system 120, 125, and 130 (e.g., by usingpositioner, 163 to move the system 100 toward the object 105). In thisspecific embodiment, secondary positioner 160 may also be adjusted tomodify the convergence (or divergence) of light directed from the lens120 and towards the object 105, such that light reflected or refractedfrom a desired subregion of second surface 105 b is delivered towavefront sensor 137, while a majority (i.e., ≧50%), or even perhaps asubstantial majority (i.e., ≧90%), of light from first surface 105 a isnow blocked by spatial aperture 125 from reaching wavefront sensor 137.The correct position can be found, for example, by monitoring the focalspot brightness on the detector 150 and searching for a secondbrightness peak, or by looking for some feature in the wavefront asreconstructed by wavefront sensor 137. This may be the position wherethe collimation of light into the wavefront sensor 137 has reached apredetermined value or even where the light is completely collimated. Atthis time, the reflection from front surface 105 a is not in focus atspatial filter 125 and so spatial filter 125 blocks a majority or asubstantial majority of this light.

In one embodiment, surfaces 105 a and 105 b are measured by making twopasses, one over each of the two surfaces 105 a, 105 b (moving system100 and/or object 105 goniometrically as described earlier andillustrated in FIG. 2), and then calculating the thickness of object 105from the amount that positioner 163 was moved between the two passes.The surface shape of front surface 105 a and index of refraction of thematerial comprising object 105 are taken into account when determiningthe shape of second surface 105 b.

In another embodiment, surfaces 105 a and 105 b are measured bysequentially in each subregion by moving positioner 163 in the directionapproximately normal to the surfaces, then moving to a new subregion andrepeating the measurement of both surfaces.

FIGS. 3A-B illustrate two exemplary arrangements for a geometricmeasurement system which may be employed for geometric measurementsystem 100. The arrangements of FIGS. 3A-B each include: light emittingelement 10 (e.g., an LED or diode laser in the visible, near-infrared,infrared, or ultraviolet wavelength bands of the electromagneticspectrum) and collimator 15 as a light source; beamsplitter 20;microscope assembly 22 including image relay lens 25, pinhole (aperture)30 (not visible in FIGS. 3A-B), objective lens 35; and sensor 60,comprising an optical element 50 and a detector array (e.g., acharge-coupled device (CCD)) 55. Element 45 is an object undermeasurement.

Operationally, light from light emitting element 10 is collected bycollimating lens 15 and projected through beamsplitter 20. This light isfurther collected by image relay lens 25 and focused onto pinhole 30 andrecollected by microscope objective lens 35. This produces a small beam,coincident with a desired subregion of object 45, that is then projectedonto the highly curved surface of object 45 that is being measured.Light from both surfaces of object 45 may be reflected from object 45and collected by the objective lens 35. However, the shape of object 45will cause the light from the surface that is not being measured toarrive at the objective lens 35 at significantly different divergencefrom the light reflected off the first surface that is being measured.The light from the surface not being measured thus arrives at aperture30, which is arranged to be about one focal length away from theobjective lens 35, and creates a fairly large spot at this plane. Thusaperture (pinhole) 30 spatially filters a majority (i.e., ≧50%) of thelight from the unwanted surface that is not being measured from reachingsensor 60. Beneficially, aperture 30 spatially filters a substantialmajority (i.e., ≧90%) of the light from the unwanted surface that is notbeing measured from reaching sensor 60. The light that passes throughaperture 30 then is recollected by relay image lens 25, and reflects offbeamsplitter 20 onto sensor 60.

In the case of a physical implementation of geometric measurement system100, then sensor 60 may be a Shack-Hartmann wavefront sensor, whereinoptical element 50 is a lenslet array that generates light spots thatare focused on detector array 55. In that case, detector array 55detects the focal points of the light spots produced by lenslet array 50to determine a wavefront of light received back from object 45.Beneficially, the output of detector 60 is provided to a processor (notshown in FIGS. 3A-B), such as processor 170 in FIGS. 1A-B. Wavefrontsfrom a plurality of subregions of object 45 are then stitched togetherto form a combined wavefront for a larger region (perhaps an entiresurface area) of object 45, as described above.

In some systems, it may be advantageous to mount relay lenses 25 and 35in an arrangement that would permit adjustment of their relativespacing. This would allow the system to adjust the base defocus to matchthat of the local region of the part to be tested. For highly aberrated,aspheric, or rapidly varying parts this may be advantageous. Otherarrangements are also possible, and may be employed by those that areskilled in the art.

Various modifications to the arrangements shown in FIGS. 3A-B arepossible, and some of these will be described in further detail belowwith respect to other embodiments of a geometric measurement system.

FIGS. 4A-C illustrate geometric measurement instrument 400, including agoniometer, that may be one structural embodiment of the arrangement ofFIG. 3A.

In FIGS. 4A-C, the elements depicted in FIGS. 3A are shown mounted on amoving platform 65. In this case the object under test 45 is mounted ina test cell 40 which is arranged so that it can rotate freely undercomputer control. Light source 10, collimating lens 15, beamsplitter 20,the microscope objective assembly, and sensor 60 are mounted on a commonplatform and held rigidly in place. Beneficially, the platform may berapidly rotated about its axis of symmetry.

In one case, geometric measurement instrument 400 may be an embodimentof geometric measurement system 100. In that case, sensor 60 is awavefront sensor, beneficially a Shack-Hartmann wavefront sensor(although a moiré deflectometer, a Tscherning aberrometer, or otherappropriate sensor could be employed instead). Also in that case,geometric measurement instrument 400 measures only one surface of object45 at time and filters the light from the other surface. So it isnecessary to have a stage the can be adjusted so that the appropriateplane is correctly imaged by the optical system. Accordingly, adjustment70 permits adjustment of the radius of curvature that can be correctlyread. The overall positioning of geometric measurement instrument 400 isaccomplished with the goniometric part 75 controlled through actuator80. This rotates the measurement head through an angle “goniometrically”about the center of curvature of some axis of object 45. Since the part40 is also rotated by rotating holder 45, the entire part may be scannedby rotating the part with holder 45 through on full revolution whilemeasuring the subregions with the sensor 60, then adjusting thegoniometer by an incremental rotation, rotating the part through a fullrevolution while measuring, etc.

FIGS. 5A-C are front views illustrating operation of geometricmeasurement instrument 400 of FIGS. 4A-C, including a goniometer. It canbe seen that geometric measurement instrument 400 measures only a smallsubregion of object 45 at a time. Beneficially, geometric measurementinstrument 400 is arranged with encoders on the motor axes. In thisembodiment it is possible to use these encoders to issue pre-arrangedtriggers to a processor (e.g., processor 170 of FIGS. 1A-B) at certainstage positions or angles. The triggers initiate the action of sending apulse of light from light emitting device 10 and detecting the receivedlight from object 45 at sensor 60. Beneficially, light emitting device10 and sensor 60 are synchronized together. It is also possible to haveonly light emitting device 10 or only sensor 60 operate in a pulsedmode.

FIG. 6 illustrates still another embodiment of a geometric measurementsystem 600 for determining at least one geometric characteristic of anobject 604, and an associated method of determining at least onegeometric characteristic of the object 604, using a phase diversitysensor.

Geometric measurement system 600 includes a light source 610 (or othersource of electromagnetic radiation); a beamsplitter 620; an opticalsystem 630; an optical element (e.g., lens and/or diffractive opticalelement) 640; a detector 650; a positioner 660; and a processor 665.

Optical element 640, detector 650 of electromagnetic radiation, andpositioner 660 form a phase diversity sensor. The phase diversity sensoris a wavefront sensor that tracks the distribution of light intensityfrom an initial pupil through the measurement of the irradiancedistribution at a number of discrete planes.

Operationally, an input wavefront 605, which can consist of light thathas been reflected from multiple surfaces of object 604, is incidentupon optical element 640. Optical element 640 collects the light anddirects it towards a focus. However, since there are two (or more)fields present in wavefront 605, the light will create two (or more)separate optical beams 633 and 637 which reach focus at different pointsalong the z-axis. By acquiring and recording multiple irradiancedistributions at different planes 622, 624 and 626 (and others asneeded) using positioner 660, the essential information about how thelight propagates from plane to plane is used to determine the incidentwavefront 605. In general it takes measurement in at least two planes,but measurement in more planes may give better analysis of the data.

In the case where object 604 to be measured is a contact lens having twosurfaces, optical element 640 receives light from the first and secondsurfaces of object 604 and produces a first light beam corresponding tolight from the first surface and a second light beam corresponding tolight from the second surface. Detector 650 has a radiation sensitivesurface. Detector 650 receives the first and second light beams anddetects the intensity of incident radiation on the radiation sensitivesurface from the first and second light beams. Detector 650 produces anoutput that provides a measure of the intensity of the incidentradiation. Positioner 660 adjusts relative positions of optical element(e.g., lens) 640 and light intensity detector 650. Processor 665determines wavefronts of the light from the first and second surfaces ofobject 604 based on the output of light intensity detector 650 at aplurality of different relative positions.

One advantage of geometric measurement system 600 is that it can measuretwo surfaces of object 640 practically simultaneously and determine boththe radius of curvature of each surface and the separation between thesurfaces (thickness).

In general it may be inconvenient to make measurements while moving adetector or using multiple beam splitters to dissect the light inmultiple directions. Thus it may be preferable to separate the planes ofthe optical beams across the detector instead of moving the detector.

Accordingly, FIG. 7 illustrates yet another embodiment of a geometricmeasurement system 700 for determining at least one geometriccharacteristic of an object 704, and an associated method of determiningat least one geometric characteristic of the object 704, using a phasediversity sensor.

Geometric measurement system 700 includes a light source 710; abeamsplitter 720; an optical system 730; a diffractive optical element740; a light intensity detector 750; and a processor 765. Beneficially,diffractive optical element 740 includes a diffraction grating 742configured to provide a plurality of diffraction orders and a lens 744,which could be combined into a single physical component.

Operationally, an input wavefront 705, which can consist of light thathas been reflected from multiple surfaces of object 704, is incidentupon diffraction grating 742 which has some defocus fringes added to thegrating lines. Light that is diffracted by this grating will bediffracted into a +1 diffraction order 770 and a −1 diffraction order780 (and other orders depending on the exact structure of the grating).Some light will be undiffracted and hence stay in a zeroth diffractionorder 775. In one example, the +1 order 770 has an effective negativefocal power and the light spreads but also has net tilt, and the −1order 780 has a positive focal power and so the light is concentrated,also with net tilt in the other direction. Optical element (e.g., arefractive or diffractive lens) 744 is included to create a compactinstrument, but can be omitted at the expense of a resultantly longerinstrument. As noted above, is also possible to build the power of thelens into diffraction grating 742. Thus the light that is collected at asingle plane 725 has three different, spatially separated images. Thefirst image 770 is light that propagates past light intensity detector750. It is like plane 630 in the FIG. 6. Light from the 0 order 775 isat the main focus and is similar to plan plane 625 in the FIG. 6, whilelight from the −1 order 780 is analogous to plane 620. Here, the imagesare spatially separated and therefore may conveniently be acquiredsimultaneously. This arrangement may find particular benefit when one ofthe surfaces of object 704 has a particularly weak reflection. Forexample, one of the surfaces may have an anti-reflective coating or maybe in contact with another element (not shown) that has a similarrefractive index to that of object 704. Such may be the case when theobject is the cornea of an eye or part of a compound lens, such as anachromat lens.

By processing the sub images mathematically, the reflected wavefrontsfrom both surfaces of an object (e.g., a contact lens) can bedetermined. With a more sophisticated diffractive optic 744 it ispossible to create even more images and hence derive a more accurateestimate of the incident wavefronts. Further details of the calculationof a surface shape using a phase diversity sensor may be found inGreenaway et al. U.S. Patent Publication 20060175528, the entirety ofwhich is hereby incorporated herein by reference in its entirety as iffully set forth herein.

Beneficially, the exemplary arrangements shown in FIGS. 3A-B may beemployed for geometric measurement system 700, with the modificationthat microscope assembly 22 omits the aperture (pinhole) 30.

In that case, light is injected via beamsplitter 20 and passes throughmicroscope assembly 22 where it is directed onto the surfaces of object45. The optical head rotates in a goniometrical fashion about the focalplane of object 45 and performs the measurement with the assistance ofsensor 60, which in this case is a phase diversity sensor. Sensor 60comprises a CCD camera with a lens and diffraction grating placed infront; so, conceptually it looks very much like a wavefront sensor. Thephase diversity sensor uses a diffraction grating with a speciallycurved grating field to create images before and after a focal plane.This allows different parts of a 3D object to be measuredsimultaneously.

FIG. 8 shows a block diagram of yet another embodiment of a geometricmeasurement system 800 for determining at least one geometriccharacteristic of an object 805, and an associated method of determiningat least one geometric characteristic of the object 805, using a whitelight interferometer.

Geometric measurement system 800 includes: a structure 810 having areference surface with a known curvature; a stage 820 adapted to holdobject 805; an optical fiber 830; a collimating lens 840; and aninterferometer 850. Interferometer 850 includes: a light source 815, adetector 825, a mirror 835, a beamsplitter 845, and a moving stage orpositioner 855 on which mirror 835 is mounted.

Light source 815 may be a superluminescent diode (SLD) or other broadband source. Beneficially, light source 815 outputs light spanning orsubstantially spanning the visible spectrum (i.e., “white light”).

Operationally, light source 815 generates light having a broad spectralbandwidth and provides the light to beamsplitter 845. Beamsplitter 845divides the light into a first portion and a second portion. The firstportion of the light is provided via optical fiber 830 and collimatinglens 840 to illuminate object under test 805 and the reference surfaceof structure 810. At least some of this light is reflected and/orrefracted by object 805 and the reference surface of structure 810 backthrough collimating lens 840 and optical fiber 830 to detector 825, viabeamsplitter 845. Meanwhile, the second portion of the light frombeamsplitter 845 is provided to illuminate mirror 835. Mirror 835reflects at least some of the second portion of the light to detector825 via beamsplitter 845.

Detector 825 is adapted to output a signal indicating when an opticalpath length traveled by the first portion of the light from beamsplitter845 to detector 825 is the same as the optical path length traveled bythe second portion of the light from beamsplitter 845 to detector 825.Fringe contrast will be obtained only when those distances traveled bylight in the two arms of the interferometer exactly match. By scanningmirror 835 in the reference arm, a signal will be obtained every timethe reference arm distance matches the distance to the surface of object805 from which light is being reflected/refracted.

Accordingly, an optical path length traveled by the second portion ofthe light from the beamsplitter, to mirror 835, and back throughbeamsplitter 845 to detector 825 is adjusted until detector 825 outputsa signal indicating a first interference fringe caused by lightrefracted or reflected by a first surface of object 805. In theembodiment of FIG. 8, the optical path length is adjusted by movingpositioner 855 on which mirror 835 is mounted. However, other means foradjusting the optical path length are possible in place of positioner855, including attaching mirror 835 to a piezo driver or voice coilactuator.

Then, the optical path length traveled by the second portion of thelight is adjusted again until detector 825 outputs a signal indicating asecond interference fringe caused by light refracted or reflected by asecond surface of object 805.

Next, the optical path length traveled by the second portion of thelight is adjusted yet again until detector 825 outputs a signalindicating a third interference fringe caused by light refracted orreflected by the reference surface of structure 810. The referencesurface allows self-calibration of geometric measurement system 800 toassist in eliminating any errors in determining the optical path lengthtraveled by the second portion of the light in the reference arm of thesystem when an interference fringe is produced from light reflected orrefracted by a surface of object 805.

Since, as noted above, an interference fringe is only produced when theoptical path lengths traveled by the first and second portions of thelight are the same, it is possible to determine a distance to (andthereby the position of) a location on the surface of object 805 fromwhich the light is reflected or refracted by determining the opticalpath length traveled by the second portion of the light reflected bymirror 835 when the detector 835 outputs the signal indicating theoccurrence of an interference fringe. In one embodiment, this opticalpath length may be determined from a positional scale associated withpositioner 855. Alternatively, a ramp signal, for example, may be usedto drive a piezoelectric device or voice coil actuator to move mirror835 along a linear path, and the times at which detector 825 outputs thesignals indicating the interference fringes are measured to determinethe distance to (and thereby the position of) the portion of a surfaceof object 805 from which light is being reflected/refracted.

While this method described measures only a single point of an object'ssurface at a time, it can do so at fairly high bandwidth (10 kHz). It issimilar to light based radar in that a signal is obtained from eachsurface that the light encounters. Thus, there is no difficultyseparating the signals from different surfaces.

With the addition of the goniometric scheme illustrated in FIGS. 4A-Cand 5A-C, geometric measurement system 800 can be used to produceprofiles of a contact lens'geometry including base curvature, frontcurvature and thickness. In addition, by rotating the contact lens,multiple meridians can also be measured and analyzed.

Geometric measurement systems as described above may be employed formeasuring a variety of objects, including for example: molds, drycontact lenses in molds, contact lenses in a fixture, intraocular lenses(IOLs), IOL molds, lenses, aspheric lenses, plastic molds, mirrors,human or animal corneas, and other objects, particularly but not limitedto objects having one or more highly curved, potentially aspheric andnon-symmetric surfaces and/or one or more surfaces that passes asubstantial amount of light (e.g., more than 10% of incident light, andmore typically more than 50% of incident light) therethrough.Beneficially the system can be manually loaded, or automated. Alsobeneficially, the system will test the presented object, display theresults, record the surface shape, and save the data to a data storagedevice (e.g., memory and/or a disk drive, etc.). Each measurement can becorrelated to a part number and batch ID, and/or any other pertinentinformation, as it is delivered to the system.

Beneficially, system components are enclosed inside a housing providinga controlled environment inside the system work envelope. All of thestages and critical system components are mounted to a solid basecapable of providing thermal and optical stability, thus insuringmeasurement accuracy.

While preferred embodiments are disclosed herein, many variations arepossible which remain within the concept and scope of the invention.Such variations would become clear to one of ordinary skill in the artafter inspection of the specification, drawings and claims herein. Theinvention therefore is not to be restricted except within the spirit andscope of the appended claims.

1. A method of determining at least one geometric characteristic of anobject having a first surface and a second surface, where at least oneof the first and second surfaces passes a substantial amount of lighttherethrough, the method comprising: (a) adjusting a positionalrelationship between a first surface of the object and a light source toilluminate a subregion of the first surface of the object, whereby aportion of light illuminating the subregion of the first surface of theobject passes through the object to the second surface of the object;(b) delivering light from the subregion of the first surface of theobject to a wavefront sensor while blocking a majority of light from thesecond surface of the object from reaching the wavefront sensor; (c)determining a wavefront of light received from the subregion of thefirst surface with a wavefront sensor; (d) repeating steps (a) through(c) for a plurality of different subregions spanning a measurementregion for the first surface of the object, where adjacent subregionshave an overlapping portion; (e) stitching together the wavefrontsdetermined in each execution of step (c) including derivatives of thewavefronts in the overlapping portions, to construct a wavefront oflight received from the measurement region of the first surface of theobject; and (f) determining at least one shape parameter of the firstsurface of the object from the constructed wavefront.
 2. The method ofclaim 1, wherein adjusting a positional relationship between a firstsurface of the object and a light source to illuminate a subregion ofthe first surface of the object includes at least one of rotating theobject with respect to the light source, and rotating the light sourcewith respect to the object.
 3. The method of claim 1, wherein adjustinga positional relationship between a first surface of the object and alight source to illuminate a subregion of the first surface of theobject includes at least one of tilting the object with respect to thelight source and tilting the light source with respect to the object. 4.The method of claim 1, wherein determining the wavefront of lightreceived from the subregion of the first surface with a wavefront sensorcomprises: delivering the light received from the subregion of the firstsurface to a light spot generator; and detecting positions of focalpoints of light spots from the light spot generator.
 5. The method ofclaim 1, wherein delivering light from the subregion of the firstsurface of the object to a wavefront sensor while blocking a majority oflight from the second surface of the object from reaching the wavefrontsensor comprises passing the light from the subregion of the firstsurface of the object and from the second surface of the object throughan aperture to spatially filter the light, and passing the spatiallyfiltered light to the wavefront sensor.
 6. The method of claim 1,wherein said stitching includes determining a wavefront in the overlapportions by one of: (a) using an error minimizing algorithm, and (b)averaging the wavefronts in the overlap portions of the adjacentsubregions.
 7. The method of claim 1, wherein determining at least oneshape parameter of the first surface of the object includes determininga three dimensional shape of the first surface of the object.
 8. Themethod of claim 1, wherein adjusting a positional relationship between afirst surface of the object and a light source to illuminate a subregionof the first surface of the object includes searching for a brightnesspeak at the wavefront detector.
 9. The method of claim 1, whereindelivering light from the subregion of the first surface of the objectto a wavefront sensor while blocking a majority of light from the secondsurface of the object from reaching the wavefront sensor comprisesblocking a substantial majority of light from the second surface of theobject from reaching the wavefront sensor.
 10. The method of claim 1,further comprising: (g) adjusting a positional relationship between thesecond surface of the object and the light source to illuminate asubregion of the first surface of the object; (h) delivering light fromthe subregion of the second surface of the object to a wavefront sensorwhile blocking a majority of light from the first surface of the objectfrom reaching the wavefront sensor (i) determining a wavefront of lightreceived from the subregion of the second surface with a wavefrontsensor; (j) repeating steps (g) through (i) for a plurality of differentsubregions spanning a measurement region for the second surface of theobject, where adjacent subregions having an overlapping portion; (k)stitching together the wavefronts determined in each execution of step(i) including derivatives of the wavefronts in the overlapping portions,to construct a wavefront of light received from the measurement regionof the second surface of the object; and (l) determining at least oneshape parameter of the second surface of the object from the constructedwavefront.
 11. The method of claim 10, wherein illuminating a sub-regionof the second surface of the object include passing an illumination beamthrough the first surface of the object.
 12. The method of claim 10,wherein determining at least one shape parameter of the first surface ofthe object and determining at least one shape parameter of the secondsurface of the object includes determining three dimensional shapes ofthe first and second surfaces of the object.
 13. The method of claim 1,further comprising adjusting an optical property of an optical systemdisposed in an optical path between the light source and the firstsurface of the object to focus light from the light source to illuminatea subregion of the first surface of the object.
 14. A system fordetermining at least one geometric characteristic of an object having atleast one surface that passes a substantial amount of lighttherethrough, the system comprising: a light source; a wavefront sensor;an optical system adapted to deliver light from the light source to asurface to be measured of the object, and to deliver light from thesurface to be measured of the object to the wavefront sensor, whereby aportion of the light delivered to the surface to be measured passesthrough the object to a surface of the object that is not beingmeasured; a translator adapted to adjust relative positions of the lightsource and the surface to be measured such that, at each relativeposition, the light from the light source is delivered onto a sub-regionof the surface to be measured, and light from the sub-region of thesurface to be measured is delivered to the wavefront sensor, thetranslator adjusting the relative positions such that adjacentsub-regions have an overlap portion; and a processor adapted to stitchtogether wavefronts measured by the wavefront sensor for differentsub-regions of the surface to be measured at the relative positionsprovided by the translator, including using derivatives of wavefronts inoverlap regions, to construct a wavefront of light received from ameasurement region of the surface to be measured, wherein the opticalsystem includes a spatial filter adapted to block a majority of lightfrom the surface of the object not being measured from reaching thewavefront sensor, and wherein the translator is also adapted to adjust adistance between the spatial filter and the surface to be measured ofthe object.
 15. The system of claim 14, wherein the wavefront sensor isa Shack-Hartmann wavefront sensor.
 16. The system of claim 14, whereinthe wavefront sensor is one of a Hartmann wavefront sensor, a moiredeflectometer, a Tscherning aberrometer.
 17. The system of claim 14,wherein the optical system comprises two lenses, wherein the spatialfilter is disposed in an optical path between the two lenses.
 18. Thesystem of claim 14, wherein the translator adjusts the relativepositions in three dimensions.
 19. The system of claim 14, wherein thetranslator includes one of means for rotating the light source and meansfor rotating the object.
 20. The system of claim 14, wherein thetranslator includes one of means for tilting the light source and meansfor tilting the object.
 21. The system of claim 14, wherein the spatialfilter is adapted to block a majority of light from the surface of theobject not being measured from reaching the wavefront sensor.
 22. Amethod of determining at least one geometric characteristic of an objecthaving a first surface and a second surface, the method comprising: (a)adjusting a positional relationship between a first surface of theobject and a light source to illuminate a subregion of the first surfaceof the object, including at least one of: rotating the object withrespect to the light source, rotating the light source with respect tothe object, tilting the object with respect to the light source, andtilting the light source with respect to the object; (b) deliveringlight from the subregion of the first surface of the object to awavefront sensor; (c) determining a wavefront of light received from thesubregion of the first surface with a wavefront sensor; (d) repeatingsteps (a) through (c) for a plurality of different subregions spanning ameasurement region for the first surface of the object, where adjacentsubregions have an overlapping portion; (e) stitching together thewavefronts determined in each execution of step (c) includingderivatives of the wavefronts in the overlapping portions, to constructa wavefront of light received from the measurement region of the firstsurface of the object; and (f) determining at least one shape parameterof the first surface of the object from the constructed wavefront. 23.The method of claim 22, wherein determining the wavefront of lightreceived from the subregion of the first surface with a wavefront sensorcomprises: delivering the light received from the subregion of the firstsurface to a light spot generator; and detecting positions of focalpoints from the light spot generator.
 24. The method of claim 22,wherein delivering light from the subregion of the first surface of theobject to a wavefront sensor further includes blocking a majority oflight from the second surface of the object from reaching the wavefrontsensor by passing the light from the subregion of the first surface ofthe object and from the second surface of the object through an apertureto spatially filter the light, and passing the spatially filtered lightto the wavefront sensor.
 25. The method of claim 22, wherein saidstitching includes determining a wavefront in the overlap portions byone of: (a) using an error minimizing algorithm, and (b) averaging thewavefronts in the overlap portions of the adjacent subregions.
 26. Themethod of claim 22, wherein determining at least one shape parameter ofthe first surface of the object includes determining a three dimensionalshape of the first surface of the object.
 27. The method of claim 22,wherein adjusting a positional relationship between a first surface ofthe object and a light source to illuminate a subregion of the firstsurface of the object includes searching for a brightness peak at thewavefront detector.
 28. A system for determining at least one geometriccharacteristic of an object, the system comprising: a light source; awavefront sensor; an optical system adapted to deliver light from thelight source to a surface to be measured of the object, and fordelivering light from the surface to be measured of the object to thewavefront sensor; a translator adapted to adjust relative positions ofthe light source and the surface to be measured such that, at eachrelative position, the light from the light source is delivered onto asub-region of the surface to be measured, and light from the sub-regionof the surface to be measured is delivered to the wavefront sensor, thetranslator adjusting the relative positions such that adjacentsub-regions have an overlap portion, wherein the translator includes oneof: means for rotating the light source, means for rotating the object,means for tilting the light source, and means for tilting the object;and a processor adapted to stitch together wavefronts measured by thewavefront sensor for different sub-regions of the surface to be measuredat the relative positions provided by the translator, including usingderivatives of wavefronts in overlap regions, to construct a wavefrontof light received from a measurement region of the surface to bemeasured.
 29. The system of claim 28, wherein the wavefront sensor is aShack-Hartmann wavefront sensor.
 30. The system of claim 28, wherein thewavefront sensor is one of a Hartmann wavefront sensor, a moir{acuteover (e )} deflectometer, a Tscherning aberrometer, and a phasediversity sensor. 31-58. (canceled)